Norway is to release a Russian suspected of spying, the country's intelligence agency, the PST, has said, adding that it had withdrawn its appeal against his release.

Mikhail Bochkaryov was detained last month at Oslo airport after participating in an international seminar on digitalization in Norway's parliament, accused of having collected data on the building and its network.

Bochkaryov has denied any wrongdoing.

A Norwegian court ordered his release on October 18, after ruling that investigators had failed to substantiate their case. But Bochkaryov was kept in custody after the PST appealed the decision.

But on October 19 the agency tweeted: 'The PST has decided to withdraw its appeal. He is released today.'

PST prosecutor Kathrine Tonstad told Norwegian television: 'We continue to investigate the case. No decision has been made on whether to file any charges. He is free to go home.'

Reports had said Bochkaryov might be used as leverage in efforts to obtain the release of a Norwegian held in Russia on suspicion of spying, but the PST has denied any connection between the two cases.

Norwegian Frode Berg was arrested in April and is still awaiting trial after admitting to having helped Norwegian intelligence by acting as a courier on occasion.

Russia had demanded Oslo throw out 'the absurd charges' and release Bochkaryov, whom it identified as a member of staff in the Russian parliament's upper house, the Federation Council.